1. Field of the Invention
The present invention relates to a selection system, its selection method for voice channels, and more particularly to a selection system, its selection method for voice channels for selecting an unoccupied voice channel within a VoIP-compatible trunk package and forming voice communication paths in a switchboard having a plurality of voice over IP (VoIP) trunks for connection to the Internet.
2. Description of the Related Art
It is known that a VoIP trunk package is mounted on a telephone switchboard for connection to the Internet. There is a hardware constraint to processing hundreds of voice channels by the use of a single large-scale VoIP trunk package. In order to avert such a hardware constraint and further to enhance safety by load decentralization, usually a VoIP trunk package is mounted in the order of a few dozens of channels.
In a switchboard on which a plurality of VoIP trunk packages are mounted, calls may sometimes concentrate on a specific VoIP trunk package to keep all the voice channels in the package busy. If call control information arrives from the Internet at the VoIP trunk package on the switchboard in this state, the switchboard is judged to be busy. Such a judgment gives rise to incomplete calls, which cannot arrive at their respective destinations. The switchboard, which is a collective body of the plurality of VoIP trunk packages, cannot effectively utilize any unoccupied channel that may be available in some other VoIP trunk package.
On the other hand, two trunks accommodated in a line circuit switching network instead of the Internet are opposite each other on a one-to-one basis, and line circuits are physically connected between them. Since the opposite trunks are aware of unoccupied voice channel resources on each other, no call is initiated to an interface having no unoccupied voice channel unless the same voice channel happens to be selected. Nor does any call arrive at an interface having no unoccupied voice channel.
However, on trunks in the Internet, opposite VoIP apparatuses in the Internet are connected in an unspecified way on a one-to-N basis, resulting in different circumstances from trunks in a line circuit switching network.
Thus, on account of this unspecified connection on the one-to-N basis, the VoIP apparatus initiating a call cannot know whether or not an unoccupied voice channel is available on the destination VoIP apparatus supposed to receive that call. Furthermore, the destination VoIP apparatus, since it cannot identify the opposite call-initiating VoIP apparatus, cannot notify the call-initiating VoIP apparatus of the availability or unavailability of any voice channel resource on the part of the destination VoIP apparatus.
Therefore, even if there is an unoccupied voice channel in one VoIP trunk package or another in the whole system consisting of a plurality of VoIP trunk packages and a switchboard, that unoccupied voice channel cannot be necessarily put to effective use.